LED security sensor

摘要

A door sensor system comprising door sensor circuit and a sensor support circuit. The door sensor circuit has the anode of a first LED and the anode of a second LED coupled to a supply voltage terminal. The door sensor circuit has one or more reed switches, each with a first terminal coupled to the first LED cathode and a second terminal coupled to a sensor output terminal. The door sensor circuit has a Zener diode with a cathode coupled to the second LED cathode and an anode coupled to the sensor output terminal. The sensor support circuit is configured to generate, based on the voltage at the sensor output terminal, a first signal if the door is open, a second signal if the door is closed, and a third signal if tampering with the door sensor system is detected.

主权项

1. A door sensor system comprising:
door sensor circuit with a supply voltage terminal, a sensor output terminal, a Zener diode, a first LED (light-emitting diode), a second LED (light-emitting diode), and a first reed switch; wherein the first LED has a first LED anode and a first LED cathode, the second LED has a second LED anode and a second LED cathode, the Zener diode has a Zener diode anode and a Zener diode cathode, wherein the first LED anode and the second LED anode are coupled to the supply voltage terminal; wherein the first reed switch has a first reed switch first terminal and a first reed switch second terminal; wherein the second LED cathode is coupled to the Zener diode cathode and the Zener diode anode is coupled to the sensor output terminal; wherein the first LED cathode is coupled to the first reed switch first terminal and the first reed switch second terminal is coupled to the sensor output terminal; further comprising a sensor support circuit with a comparator circuit, wherein the sensor support circuit is configured for providing a supply voltage Vs to the supply voltage terminal of the door sensor circuit; wherein the first LED has a first LED on-voltage VO1 and the second LED has a second LED on-voltage VO2; wherein the Zener diode has a breakdown voltage VB; wherein the values for first LED on-voltage VO1, the second LED on-voltage VO2, breakdown voltage VB and the supply voltage Vs are such that the combination of the second LED on-voltage VO2 and the breakdown voltage VB is less than the supply voltage Vs and greater than the first LED on-voltage VO1; wherein the comparator circuit has a comparator input that is configured for coupling with the sensor output terminal; wherein the comparator circuit is configured to output a first signal if a voltage at the comparator input is not greater than a first comparator voltage level; wherein the comparator circuit is configured to output a second signal if a voltage at the comparator input is greater than the first comparator voltage level and not greater than a second comparator voltage level; and wherein the comparator circuit is configured to output a third signal if a voltage at the comparator input is greater than the second comparator voltage level.